How to make biochar from an outdoor woodburning boiler

Biochar is getting alot of attention lately as a technique both for improving soil, for growing plants, and for sequestering carbon dioxide, so I’ve been wanting to learn how to make it. I attended Yarrow’s biochar conference in NH and came home to experiment with my outdoor wood boiler and lo and behold, the universe blessed me with a way to quickly make it without special tools or extra inner-barrels. I plan to eventually put up a youtube video of how to do it but thought the discovery was too important really to wait. We need change in this world NOW. So here it goes.

To make biochar:

  1. burn large 5-6 logs, 3-4′ in length in center of stove as usual.
  2. cut 2-4″ thick slices off logs in the woodpile and make about 12 slices. The logs can be any diameter, just cut them thinly to 2″ or so.
  3. pile those thinner slices on both sides of the main fire, so those slices are against the stove sides of the boiler, in piles all down the side of the boiler
  4. open up 4-8 hours later. The main fire baked the thin slices into char due to (I am guessing here) increased surface area of the slices beyond the regular logs. If you see wood grain in the char, bake longer. If the slices have crumbled into tinier black pieces, its char and time to remove. If you probe a slice and it crumbles, its ready too.
  5. since the char is on the sides, its easy to shovel out
  6. shovel, dump outside and douse with water
  7. all crushable char is good, or so I’ve been told. 99% of all my char was good so far. Treat char with compost tea or equiv for a week or two. Not sure what is optimum tea time.

one burn cycle of this makes about 3 gallon bucket and I bet experimentation with the amount of log slices, production could be easily expanded to 5 gallon volumes of char every 4-8 hours. When crushed, it goes a long way in the beds. I couldn’t wait the two weeks tea time which was risky, but mixed char in with my transplants after a few days of tea. I haven’t charred every square foot of my beds yet, but char is local near every plant root, at least. I am watering with compost tea from time to time too to make sure the soil-embedded char keeps getting inoculated. I have nothing to compare the char beds to as I have no control beds but everything looks healthy and green.

One person at the biochar conference told me the oxygenated char, which is my char, is actually better than the kind of char you smother and choke away from oxygen (the word escapes me here…I think it’s “Pyrolysis”).

I’m sure you know if char isn’t aged or put with tea for a short time, it will set back a garden for several weeks so I am trying to be careful and patient with the production.
Let me know if this technique works for any of you, please.

Feel free to post a comment below if you want to start a discussion. I have no evidence that biochar’s actually going to do me any good. I am taking a leap of faith with science, I’ve seen A/B comparisons of garden beds with and without char, and I’m just going ahead and putting it in all my beds. If biochar indeed is what scientists claim it to be I am excited because I’m constantly building soil for my organic beds. To be able to store what would be leaching away from my beds is very exciting. I know I’m getting old when something like that is exciting.

FarmerKB with some home-made biochar

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